It is known to produce acrylic esters by carrying out a transesterification reaction between an acrylate of a light alcohol (known as light acrylate) and a heavy alcohol.
This reaction is an equilibrated catalyzed reaction with generation of light alcohol, according to the formula (I):CH2═CH—COOR1R2—OHCH2═CH—COOR2+R1—OH
It is necessary to remove the light alcohol produced during the reaction in order to shift the equilibrium in the direction of the production of the acrylic ester.
This reaction is generally accompanied by side reactions which produce impurities which is necessary to remove for the purpose of obtaining the acrylic ester with a high purity satisfying the technical requirements related to its final use as monomer to manufacture polymers which can be used in numerous fields of application.
Furthermore, for obvious economic reasons, the economically upgradeable products present in the crude reaction mixture, in particular the unreacted reactants and the catalyst, are, as far as possible, recycled within the process.
For these purposes, a separation/purification process comprising a combination of distillations, extractions and/or separations by settling is generally performed, which process is simultaneously relatively complex to carry out, in particular as a result of the presence of azeotropic mixtures, and expensive energetically.
Various transesterification processes for producing acrylic esters have already been described in the prior art.
Mention may be made, for example, of the document U.S. Pat. No. 7,268,251, in which the reaction effluent from the transesterification is treated in the following way:                either most of the desired acrylic ester is first of all separated and is subsequently isolated from the catalyst used by distillation (separation of catalyst),        or it is first of all isolated from the catalyst used by distillation (separation of catalyst) and subsequently most of the acrylic ester is separated,        and, subsequently, the compounds having a lower boiling point than that of the desired acrylic ester are separated by distillation of the mixture obtained (separation of low-boiling-point substances) and subsequently the acrylic ester is distilled (distillation in the pure state).        
This process requires the use of at least four distillation or rectification columns, including an evaporator in order to separate the catalyst, generally a titanium alkoxide.
Even if the process described in the document U.S. Pat. No. 7,268,251 relates to the manufacture of alkyl acrylates by transesterification starting from an alkyl acrylate and from an alcohol exhibiting a chain length greater by at least one carbon with respect to the alkyl chain of the starting acrylate, this process is illustrated only with the manufacture of dimethylaminoethyl acrylate from dimethylaminoethanol and methyl acrylate or ethyl acrylate in a cascade of two reactors.
It turns out that the process described in the document U.S. Pat. No. 7,268,251 is complicated to carry out on the industrial scale, as a result of the optimization of the operating conditions of the succession of the four distillation/rectification components, in order to obtain a product of high purity and a satisfactory productive output.
The document U.S. Pat. No. 6,977,310 describes a process for the continuous manufacture of (meth)acrylic acid alkyl esters from methyl(meth)acrylate and from a C2-C12 alcohol in the presence of a tetraalkyl titanate as transesterification catalyst. This process consists in subjecting the reaction mixture to a distillation under reduced pressure which separates the easily volatile compounds (unreacted reactants) and then the resulting fraction exiting at the column bottom, comprising the ester produced, the catalyst, the polymerization inhibitors and the high-boiling-point byproducts, is sent to a vacuum distillation stage which makes it possible to recover, at the top, the ester produced of high purity. According to this process, illustrated solely with the manufacture of butyl methacrylate or of isobutyl methacrylate, the desired methacrylate occurs in the bottom stream from the first distillation column under reduced pressure before being separated from the catalyst and purified.
The document EP 960 877, on behalf of the applicant company, illustrates another process for the manufacture of dimethylaminoethyl acrylate, more generally of dialkylaminoalkyl acrylate, by transesterification starting from dimethylaminoethanol and from methyl acrylate or ethyl acrylate.
This process consists of a removal of the catalyst and heavy products (tailing), followed by a removal of the light compounds (topping) and by a final rectification of a crude transesterification reaction mixture obtained using a catalyst chosen from tetrabutyl, tetraethyl and tetra(2-ethylhexyl) titanates. This process thus exhibits the advantage of comprising only three distillation columns in the purification train for the reaction mixture.
However, the process described in the document EP 960 877 is not applicable to the manufacture of a long-chain alkyl acrylate, for example 2-octyl acrylate, by transesterification reaction of a light acrylate with 2-octanol. This is because the transesterification of the titanates, either with a light alcohol released during the reaction or with the starting 2-octanol, brings about the appearance of impurities, such as butyl acrylate or 2-ethylhexyl acrylate, in the reaction mixture or in the light ester/light alcohol azeotropic mixture and complicates the purification of the 2-octyl acrylate.
A need thus still remains to have available a process for the manufacture of 2-octyl acrylate which exhibits a productive output compatible with manufacture on the industrial scale and which results in a 2-octyl acrylate meeting the purity requirements related to its final use, in particular with regard to the possibility of using this monomer in the manufacture of latexes having a low content of volatile organic compounds.
The applicant company has sought to solve the various problems of the abovementioned processes, in particular those related to the use of 2-octanol in the transesterification reaction, in order to produce 2-octyl acrylate of very high purity with a high yield, while including the recycling of the economically upgradeable products, such as the unreacted reactants and the catalyst.
The solution provided consists in using ethyl titanate in solution in 2-octanol or 2-octyl titanate as transesterification catalyst and in employing a purification train comprising a preliminary separation of the catalyst by distillation, followed by purification using at least one distillation column.
The present invention makes it possible in addition to produce an acrylic ester comprising carbon of renewable origin related to the use of the 2-octanol, which is an alcohol derived from plant matter.